1. Field of the Invention
The present invention relates, in general, to vehicle lifts having vertical columns in which lift arms are supported in cantilever fashion therefrom for supporting vehicles such as cars, trucks, and the like, in service stations, repair centers, and the like, and in particular, to low clearance vehicle lifts having such vertical columns and cantilevered lift arms.
2. Description of the related art
Dual-column hydraulic lifts are often used to raise and lower vehicles such as cars, trucks, and the like, in service stations, repair centers, etc. Typically, such dual-column lifts have a hydraulic cylinder within each lift column, with a chain or wire rope extending from the column base plate over a chain wheel or pulley atop the hydraulic cylinder and down to the carriage mounted on the lift column so that reciprocation of the pistons of each lift column's hydraulic cylinder causes the carriage to raise and lower. Such an arrangement is expensive to manufacture, requires periodic maintenance and lubrication, and also requires some sort of a slack cable or chain safety device to stop downward movement of the carriage when and if the cable or chain breaks.
Another known construction of dual-column lifts utilizes a telescoping (multi-section) hydraulic cylinder within each lift column to raise and lower the carriage mounted on each lift column. Telescoping hydraulic cylinders are known to be more expensive than non-telescoping, i.e., single section, hydraulic cylinders, and require some sort of speed control device so that the smaller section or stage does not raise and lower too quickly with respect to the other stages.
Additionally, dual-column lifts such as U.S. Pat. No. 5,009,287 are known that have a hydraulic cylinder within each lift column that directly raise and lower the carriage on each lift column without chains or cables. However, in such a i design, like the non-telescoping chain or cable-equalized lifts, the hydraulic cylinder, when collapsed or fully retracted, is approximately one-half the vertical lifting distance of the lift. Consequently, the piston rods of the hydraulic cylinders, when fully extended to raise a vehicle a given lifting height, rise to a substantial vertical distance from the floor, thereby preventing the use of such a dual-column lift in an area with low ceiling clearance.